Acid-in-oil emulsions are typically used to stimulate or enhance hydrocarbon production in existing carbonate reservoir rock formations, such as limestone, dolomite or calcareous-magnesium. Typically, the emulsified acid enters the formation and where employed successfully it creates a barrier causing the acid to release slowly at a distance from the well-bore and to react more slowly. The reaction of the released acid with the formation rock takes place simultaneously at different places inside the formation, resulting in channels that are joined together to form continuous wormholes.
The emulsions also can limit corrosivity of the acid on downhole and other metal equipment because the oil external phase is non-corrosive. When pumping the acid-in-oil emulsions through steel tubing and piping, a corrosion inhibitor is usually added to reduce the corrosive effects of the acid. In operation, the corrosion inhibitor coats the steel surfaces as the emulsion is pumped into the well-bore and the surrounding rock.
Even so, emulsified acids reach useful limits at temperatures greater than about 300° F. because the emulsions become destabilized at such temperatures. As a result of destabilized emulsions, acid exposure increases and corrosion problems can thereby ensue.